I have a 66 GTO 4 SPEED with a 1973 400 block and 93 heads, stock rear end gears. I am gioing to have the engine rebuilt and I was wondering if anyone can recommend what cam lift I should have installed. I want a nice Lobe and I love the muscle car ( cam sound) when a car is at a stop. would like to keep gears stock and drive on the freeway. any help would be appreciated.

Also, with a 400 block, you have 400 pistons, which have their valve reliefs cut for a '67-up head. The 093 head is a '66 GTO closed chamber head, with different valve angles. To put it simply, a big cam in this engine will cause the valves to hit the pistons. You should be able to run an 068-type of camshaft without issue. Also, be advised that you will need to use race gas or boosted fuel with these heads...if they are 093's. They are only about 64-69cc, and are ping-monsters. My advice would be dished pistons, forged rods, and decent heads. AFTER you decide the car's main purpose. Comp cams XE 262-268 cams work well with a nine to one 389 or 400.

Also, with a 400 block, you have 400 pistons, which have their valve reliefs cut for a '67-up head. The 093 head is a '66 GTO closed chamber head, with different valve angles. To put it simply, a big cam in this engine will cause the valves to hit the pistons. You should be able to run an 068-type of camshaft without issue. Also, be advised that you will need to use race gas or boosted fuel with these heads...if they are 093's. They are only about 64-69cc, and are ping-monsters. My advice would be dished pistons, forged rods, and decent heads. AFTER you decide the car's main purpose. Comp cams XE 262-268 cams work well with a nine to one 389 or 400.

IMHO

I would move from 1966 93 heads (1.92/1.66) to 67-70 (72-75 cc) heads with 2.11/1.77 valves. Before buying dished pistons try .051" or .060" head gaskets to lower the CR.

Another appropriate question would be, how much are you willing to spend? If you go much over stock lift there's a point where things start to rapidly snowball on you. You have to run different valve springs because the stockers aren't strong enough to keep the lifters on the lobes, and they also go into coil bind before the valves can get fully open - so you need taller/stronger springs. To install the taller/stronger springs you have to have the spring seats in the heads machined to make room for them. You probably have to have the tops of the valve guides cut down to keep them from getting hit by the bottoms of the retainers, and cutting them means different valve stem seals. All that also puts you into territory where you must have an adjustable valve train, so then you need poly-locks. And then the bottleneck studs are suspect because they tend to break at the neck with higher spring pressures ---- so you replace them with 7/16" studs. It's kinda silly to spend all that on the top of the motor and still run stamped steel rocker arms, so next you pop for roller rockers. The maybe some stud girdles... then new valve colvers because the factory ones won't clear --- or you have to find some spacers. The you need custom length pushrods after all the other changes...

Get the idea?

I'm not trying to talk you out of it, just be aware there's a lot more to it than just swapping out the cam shaft.

There is no reason to run 389 heads on a 400 block, IMO. They are inferior in every way to the later heads. I am running them on my '65 GTO because it's a '65 389, and that's the only reason. I need race gas, too. If the engine in question was indeed a 389, then yes, for appearance sake. But for a 400, it would be a huge improvement to install 400 spec heads....and go from there. Lots of previous threads on this topic, and "Mr P-body" (Jim Lehert of Central Virginia Machine) can help you pick the right parts and services for a good running, long lasting engine. Or, since it's a '66 and you seem to have all the correct parts except a block, locate a '66 389 and build it up with low compression pistons. Done a couple now, and they run great.